Make an Enemy a Friend

Sometimes a story needs a temporary antagonist until the real antagonist has had time to get close to the hero.

Take Zoolander. Mugatu is somewhat removed from Zoolander for the first while. So to fill the space with tension until Mugatu can come into play, Zoolander's most-hated is his model-rival Hansel. Without this antagonism in the first act, there wouldn't have been much going on. As is, we get the excitement of the walk-off while Mugatu plots. And the beauty of a Hansel is, you can turn him into an ally on a dime.

Besides, Zoolander without Hansel is like a funeral without a good eugoogaly.